Many hybrid and electric vehicles receive at least a portion of motive power from batteries. The batteries may be comprised of battery cells that are combined in series and parallel to provide power to an electric motor that propels the vehicle. During battery discharge, the duration of a discharge cycle may be limited by an amount of charge retained by the battery cell that has the lowest charge capacity. For example, if a first and second battery cell of a battery are charged to the same level, and the first battery cell has a charge capacity of 0.25 amp-hours while the second battery cell has a charge capacity of 0.3 amp-hours, the first battery cell will reach a predetermined recharge voltage (e.g., a predefined voltage at which battery cell discharge is stopped and recharging is initiated) before the second battery cell if both battery cells are discharged at the same rate. As a result, the battery discharge cycle is cut short by the lower capacity battery cell reaching the recharge voltage before the higher capacity battery cell reaches the recharge voltage. Once the lower capacity battery cell reaches the recharge voltage the battery discharge cycle is stopped so that the lower capacity battery cell is not degraded. Consequently, the battery may have a significant but unusable amount of stored charge in higher capacity battery cells that is unavailable during a discharge cycle. Therefore, the range of the vehicle that is operating under power from the battery may be limited.
The inventors herein have recognized that additional battery capacity may be available to power battery loads if the state of each battery cell is controlled during a battery discharge. Accordingly, the inventors herein have developed a method for extending the useable capacity of a battery pack, said battery pack comprising a plurality of battery cells, comprising: discharging a battery cell via a first current path during a battery discharge cycle; and charging said battery cell via a second current path during said battery discharge cycle.
A battery discharge cycle may be prolonged by supplying charge from higher capacity battery cells to lower capacity battery cells so that the charge of the lower capacity battery cell remains above a predetermined recharge voltage for a longer period of time. For example, if two battery cells start a discharge cycle from the same voltage level, the second battery cell may provide charge to the first battery cell by way of a flyback transformer. In this way, the first battery cell may remain at a voltage that is greater than a recharge voltage for a longer period of time. When both battery cells reach the recharge voltage the battery discharge cycle may be stopped.
The present description may provide several advantages. For example, the method may increase battery discharge cycle time. In addition, the present method may increase the range of electric or hybrid vehicles. Further, the system may increase battery cell life by exercising higher amounts of battery cell capacity.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.